/*
 * strftime.c
 */

#include <stdint.h>
#include <stddef.h>
#include <time.h>
#include "ctime.h"

static char *afmt[] =
{
    "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat",
};

static char *Afmt[] =
{
    "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday",
    "Saturday",
};

static char *bfmt[] =
{
    "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep",
    "Oct", "Nov", "Dec",
};

static char *Bfmt[] =
{
    "January", "February", "March", "April", "May", "June", "July",
    "August", "September", "October", "November", "December",
};

static size_t gsize;
static char *pt;

static size_t _fmt(const char *format, const struct tm *t);
static int _secs(const struct tm *t);
static int _conv(int n, int digits, int pad);
static int _add(char *str);

size_t strftime(char *s, size_t maxsize, const char *format, const struct tm *t)
{
    pt = s;
    if ((gsize = maxsize) < 1)
        return(0);

    if (_fmt(format, t))
    {
        *pt = '\0';
        return(maxsize - gsize);
    }

    return(0);
}

static size_t _fmt(const char *format, const struct tm *t)
{
    for (; *format; ++format)
    {
        if (*format == '%')
        {
            switch(*++format)
            {
                case '\0':
                    --format;
                    break;
                case 'A':
                    if (t->tm_wday < 0 || t->tm_wday > 6) return(0);
                    if (!_add(Afmt[t->tm_wday])) return(0);
                    continue;
                case 'a':
                    if (t->tm_wday < 0 || t->tm_wday > 6) return(0);
                    if (!_add(afmt[t->tm_wday])) return(0);
                    continue;
                case 'B':
                    if (t->tm_mon < 0 || t->tm_mon > 11) return(0);
                    if (!_add(Bfmt[t->tm_mon])) return(0);
                    continue;
                case 'b':
                case 'h':
                    if (t->tm_mon < 0 || t->tm_mon > 11) return(0);
                    if (!_add(bfmt[t->tm_mon])) return(0);
                    continue;
                case 'C':
                    if (!_fmt("%a %b %e %H:%M:%S %Y", t)) return(0);
                    continue;
                case 'c':
                    if (!_fmt("%m/%d/%y %H:%M:%S", t)) return(0);
                    continue;
                case 'D':
                    if (!_fmt("%m/%d/%y", t)) return(0);
                    continue;
                case 'd':
                    if (!_conv(t->tm_mday, 2, '0')) return(0);
                    continue;
                case 'e':
                    if (!_conv(t->tm_mday, 2, ' ')) return(0);
                    continue;
                case 'H':
                    if (!_conv(t->tm_hour, 2, '0')) return(0);
                    continue;
                case 'I':
                    if (!_conv(t->tm_hour % 12 ? t->tm_hour % 12 : 12, 2, '0')) return(0);
                    continue;
                case 'j':
                    if (!_conv(t->tm_yday + 1, 3, '0')) return(0);
                    continue;
                case 'k':
                    if (!_conv(t->tm_hour, 2, ' ')) return(0);
                    continue;
                case 'l':
                    if (!_conv(t->tm_hour % 12 ? t->tm_hour % 12 : 12, 2, ' ')) return(0);
                    continue;
                case 'M':
                    if (!_conv(t->tm_min, 2, '0')) return(0);
                    continue;
                case 'm':
                    if (!_conv(t->tm_mon + 1, 2, '0')) return(0);
                    continue;
                case 'n':
                    if (!_add("\n")) return(0);
                    continue;
                case 'p':
                    if (!_add(t->tm_hour >= 12 ? "PM" : "AM")) return(0);
                    continue;
                case 'R':
                    if (!_fmt("%H:%M", t)) return(0);
                    continue;
                case 'r':
                    if (!_fmt("%I:%M:%S %p", t)) return(0);
                    continue;
                case 'S':
                    if (!_conv(t->tm_sec, 2, '0')) return(0);
                    continue;
                case 's':
                    if (!_secs(t)) return(0);
                    continue;
                case 'T':
                case 'X':
                    if (!_fmt("%H:%M:%S", t)) return(0);
                    continue;
                case 't':
                    if (!_add("\t")) return(0);
                    continue;
                case 'U':
                    if (!_conv((t->tm_yday + 7 - t->tm_wday) / 7, 2, '0')) return(0);
                    continue;
                case 'W':
                    if (!_conv((t->tm_yday + 7 - (t->tm_wday ? (t->tm_wday - 1) : 6)) / 7, 2, '0')) return(0);
                    continue;
                case 'w':
                    if (!_conv(t->tm_wday, 1, '0')) return(0);
                    continue;
                case 'x':
                    if (!_fmt("%m/%d/%y", t)) return(0);
                    continue;
                case 'y':
                    if (!_conv((t->tm_year + _BASE_YEAR) % 100, 2, '0')) return(0);
                    continue;
                case 'Y':
                    if (!_conv(t->tm_year + _BASE_YEAR, 4, '0')) return(0);
                    continue;
#if 0
                case 'Z':
                    if (!t->tm_zone || !_add(t->tm_zone)) return(0);
                    continue;
#endif
                case '%':
                    /*
                     * X311J/88-090 (4.12.3.5): if conversion char is
                     * undefined, behavior is undefined.  Print out the
                     * character itself as printf(3) does.
                     */
                default:
                    break;
            }
        }

        if (!gsize--)
            return(0);
        *pt++ = *format;
    }

    return(gsize);
}

static int _secs(const struct tm *t)
{
    static char buf[15];
    register time_t s;
    register char *p;
    struct tm tmp;

    /* Make a copy, mktime(3) modifies the tm struct. */
    tmp = *t;
    s = mktime(&tmp);
    for (p = buf + sizeof(buf) - 2; s > 0 && p > buf; s /= 10)
        *p-- = s % 10 + '0';
    return(_add(++p));
}

static int _conv(int n, int digits, int pad)
{
    static char buf[10];
    register char *p;

    for (p = buf + sizeof(buf) - 2; n > 0 && p > buf; n /= 10, --digits)
        *p-- = n % 10 + '0';
    while (p > buf && digits-- > 0)
        *p-- = pad;
    return(_add(++p));
}

static int _add(char *str)
{
    for (;; ++pt, --gsize)
    {
        if (!gsize)
            return(0);
        if (!(*pt = *str++))
            return(1);
    }
}

